The objectives of this proposal are to: 1) establish the prevalence of different types of sleep disordered breathing (SDB) in a large general random sample of children; 2) identify important risk factors of SDB; (3) establish the family history of various risk factors associated with children with SDB; (4) assess the impact of SDB on clinical, psychometric and behavioral/academic outcomes; and 5) identify characteristics which will assist in identifying those children at risk for SDB for possible early intervention. Several studies evaluating select populations have suggested that various severe consequences are associated with SDB in children. These consequences include: cardiovascular complications such as pulmonary hypertension, cor pulmonale, and arrhythmia; behavioral abnormalities such as excessive daytime sleepiness, poor school performance, hyperactivity, aggressive behavior, and social withdrawal; and growth disturbances which at times are reversed by successful treatment. To date, there have been only four studies evaluating the prevalence of sleep apnea using objective sleep evaluation methods in general random samples of children. Three studies evaluated a limited age range of 6 mos to 6 yrs, while the fourth assessed a range of 2-18 years. These studies employed relatively small samples in their sleep laboratory phase (N=lO, 11, 132, and 126, respectively). Thus, they could not adequately assess clinical significance. None of these studies evaluated: general development (eg height, weight, age adjusted BMI); the effects of SDB on physical health (eg blood pressure); academic achievement; or electrophysiologic defined sleep stages as possible outcome measures. Only one study reported a possible association with daytime sleepiness and behavior. Thus, the prevalence and clinical impact of SDB in school age children is unknown. In order to establish the prevalence and clinical significance of SDB in children aged 6 - 12 years with reasonable precision, we propose to employ a protocol similar to that used to establish the prevalence and clinical significance in two previously NIH supported protocols in adults. The proposed study will employ a two-phase protocol: 1) questionnaire completed by the parents of every child enrolled in local elementary school which will assess general sleep, behavior and learning problems; 2) a random sample (n= 1,000) selected from the first sample based on risk for SDB and evaluated in the sleep laboratory to determine the presence of SDB. The second phase will receive a thorough pediatric ENT and pulmonary evaluation and school records and behavior will be assessed. The parents of this group will be interviewed for the family history of risk factors associated with SDB in children. This strategy will yield adequate power to establish the prevalence and clinical significance of SDB in children.